Magneto tunnel junction (MTJ) elements are used as magnetoresistive elements of magnetic random access memories (MRAM). The MTJ elements include a magnetic material and an insulating material such as MgO. Therefore, processing the MTJ elements by reactive ion etching (RIE) using halogen gas, which is commonly used in the semiconductor field, is difficult. If the MTJ elements are processed by RIE, a corrosion problem may be caused due to their weak resistance to corrosion. Furthermore, since the MTJ elements include many materials that are difficult to etch, etching itself may be difficult to be performed.
In order to deal with this problem, a milling process using Ar ions that is an inert gas may be employed to process the MTJ elements. However, the milling process with Ar ions physically sputters atoms. As a result, the sputtered atoms may adhere to side surfaces of the MTJ element to form a shunt path in a tunnel barrier layer of the MTJ element. This may degrade the magnetoresistance (MR), and in the worst case, cause a short-circuit failure in the device. Thus, when MTJ element is processed by milling, it is important not to cause the shunt path due to a layer of atoms adhering to side surfaces of the MTJ element.